Octagonal Type cross section RTJ ring joint gaskets are designed for flanges with standard grooves R(oval) RTJ ring joint gasket is manufactured into oval cross section,it is suit for ANSI B 16.5ASME B16.47,  series A flange,can be used in pressures up to 1000 PSI.The oval type is the only gasket that will fit a bottom  radiused groove,flanges with flat bottom v-grooves also can be accepted .

API 6A Seal Ring